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Author Topic: Roof antenna and garage door height  (Read 1183 times)
KG4VJD
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Posts: 77




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« on: April 15, 2003, 12:52:51 PM »

Well, I'm about to drill a hole on my 92 Caravan for the NMO mount and planning to install a dual band 2m/70cm 18" antenna (those with a coil of 3.5 turns at the middle).  We are also moving and will be renting a house in the future with a garage too.  Presently, we don't have a garage so whatever antenna on the roof is fine but with the new house (to be determined), we'd like to be able park the van inside the garage.  The height of the van plus the antenna is 83.2".  I think a typical garage is 7ft (84").  So, how risky is this project?  If I'm ended up taking down the antenna because of garage door height issue, then I'm not going to drill a hole on the roof.  What's your experience with this situation?

Thanks.
73, KG4VJD
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K0BG
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« Reply #1 on: April 15, 2003, 02:08:16 PM »

The height measurement doesn't sound right. I have a dual band Larsen and it's 34" long. If I were to mount it on top of my car instead of on my trunk lid, the tip would be at 91" and my car is no where near the height of a minivan (car is 57"). A little scrapping might be okay, but if your van is as tall as I think it is, it just won't scrape, it'll scrape off! Mount it on a front fender instead.

Alan, KØBG
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K5LXP
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« Reply #2 on: April 15, 2003, 02:26:17 PM »

I have one of those short dualband antennas too.  If your garage door estimate and van measurements are correct, you should be fine.  Even if you're too tall by a few inches, the worst that usually happens is to have to listen to the "twang" as you drive into the garage.  I've been listening to it for years.  Just make sure there's nothing for the antenna to catch on as it goes across.

Mark K5LXP
Albuquerque, NM
k5lxp@arrl.net
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KG4VJD
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Posts: 77




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« Reply #3 on: April 15, 2003, 02:30:45 PM »

Thanks Alan for your reply.  According to the spec, the van is 64.2" tall.  I have the dual band antenna and it is a little less than 19" tall.  The antenna is actually a one piece wire that has a 3.5 turn coil at the middle (Workman DB-1).  I believe the coil acts as a center loading 1/4 WL for 2m and becomes a phase coil for 70cm.  Therefore, I came up with a total height of 83.2".  Will it still hit the garage door?
73
Alex KG4VJD
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KG4VJD
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Posts: 77




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« Reply #4 on: April 15, 2003, 02:37:01 PM »

Thanks Mark for your reply as well.  I have been under the assumption that a typical garage door is 7ft.  Since I have not yet determined my new house yet so I think I may be taking a risk here.  I surely like to be able to use the roof as the "best" ground plane.  But if I'm going to scratch the garage door, that probably not a good idea.  I guess I may want to do a front fender mount as you have suggested.  Then I'll change to a roof mount when I have moved into the new house and the clearance is permissable.

73
Alex KG4VJD
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K0BG
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« Reply #5 on: April 15, 2003, 08:54:07 PM »

My garage measures 85 inches, but I'm with mark; I think the antenna is longer than 19" and if it isn't, it's less than unity on either band. I'd remeasure.

One thing you can do if it does hit, is to install a spring at the bottom of the whip and shorten the whip accordingly. At least this will give is a little more flexibility.

Alan, KØBG
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KG4VJD
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« Reply #6 on: April 16, 2003, 11:24:19 AM »

Thanks Alan again for your data.  I think I'm on the right track that typical garage height is about 7ft.  I guess I'm not going to do anything before I know where my new home will be.  Currently, I have a gutter mount dual band on the van which is less than an ideal location for antenna.

73
Alex KG4VJD
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WB2WIK
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« Reply #7 on: April 16, 2003, 01:12:09 PM »

You could do what I do, which is always use the NMO mount in the center of the vehicle's roof, regardless of how tall that makes it, because I can never get the vehicle in the garage, anyway!

(Especially for those first few months after moving, when the garage is full of cartons.)

I like parking in the driveway, and leaving the garage for more appropriate things like ping-pong tables, extra refrigerators, ham radio workbench and test gear, etc.  Who needs a car in there, cluttering things up?

WB2WIK/6
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KA5S
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« Reply #8 on: April 17, 2003, 08:12:24 PM »

If it's springy, it will pass the garage door OK, but it may over time show some wear from being scraped on the door.

I use *large* antennas and tilt them over.

Cortland
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AA8RF
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Posts: 67




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« Reply #9 on: April 18, 2003, 11:35:06 PM »

I also have a tilt mount for my screwdriver. I found for skip work just leaving it angled almost parallel with the ground but works just as well for HF work.

For local UHF/VHF you don't want to be too far cross polarized, but tilted may work quite well.

I park every day in a garage at work and home and leaving the whip tilted is just easier.

-Jim
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KC0OXM
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« Reply #10 on: April 21, 2003, 05:35:43 PM »

I have a '96 Dodge Caravan with the larsen dual band magmount, which is 18" tall.  My garage door is a standard 7' tall.  I hear a bit of a twang as I drive in or out, but not a big deal.

If you do find that your installation is too tall for yoru antenna, you could switch to a Comet B-10, which is only 12" and comes with an NMO mount.

Pat
KC0OXM
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KG4VJD
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Posts: 77




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« Reply #11 on: April 23, 2003, 11:15:59 AM »

Thanks for all the replies.  I'll wait until I know where my new QTH will be before I decide on roof mount or fender mount.

73
Alex KG4VJD
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N6AJR
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« Reply #12 on: May 04, 2003, 01:08:31 AM »

Bolt a flat steel or aluminum plate 2 inches wide and a couple feet long from under the frame in the back out the drivers side on the 45 degree angle . Bring it out far enough to mount an antenna.

You can bolt it or weld it on. You can run an extension up to make it tall ( with a brace to the tail light bracket) or use a tall hamstick for any band you want.

This is cheep, and it works, and when you sell it leave it or cut it off underneath.. tada.. this works on any vehicle, even those with no frame , you put a plate in the trunk and a plate outside and make a trunk sandwich to hold the antenna plat.

73 tom N6AJR
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K4MIR
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Posts: 41




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« Reply #13 on: July 20, 2003, 08:54:21 PM »

This post is several months old, so I don't know if you will read this, but I put a 1/2 wave 2 meter antenna on a remote controlled motor mount that I love.

I raise it every morning when I pull out of the garage and lower it when I go in the garage.

Works really well.  I paid about 100 bucks for the mount from HRO.

73
Mack
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KG4VJD
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Posts: 77




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« Reply #14 on: August 09, 2003, 06:21:46 PM »

Yep, I still read this post and I ended up NOT parking my van in the garrage.  It now has a NMO dual band antenna (about 18" tall) in the middle of the roof.

73 !
KG4VJD
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